Taylor Swift has had enough.

The Daily Mail has learned that the superstar singer was left devastated on Friday when she was subpoenaed as a witness in the case between Blake Lively and Justin Baldoni.

Despite putting on a brave face in Philadelphia this weekend - reportedly joining her boyfriend Travis Kelce and their respective moms for a Mother's Day lunch - it is understood that Swift, 35, has been 'completely floored' by the legal escalation and is now 'very upset'. 

And not least because she feels betrayed and 'exploited' by her longtime friend, Lively.

Up until this year, Swift counted Lively, 37, among her closest confidantes. They live just a stone's throw away from each other in New York's trendy Tribeca neighborhood, and Swift is godmother to Lively's three daughters.

But things soured in December when Lively sued Baldoni, her co-star and director in the It Ends With Us movie adaptation of the popular Colleen Hoover novel. 

Travis Kelce and Taylor Swift arrived hand-in-hand for a Mother's Day lunch in Philadelphia on Sunday

Meanwhile, Blake Lively stepped out in New York City on Saturday

Lively's sprawling complaint accused Baldoni of sexual harassment, as well as coordinating a smear campaign against her.

Then, when Baldoni countersued in January, accusing Lively and her husband Ryan Reynolds, 48, of defamation, Swift was dragged into the mix.

Contained in Baldoni's filing were screenshots of text messages and emails that named Swift. One particularly uncomfortable exchange allegedly shows Lively referring to herself as Khaleesi - a character in Games of Thrones - and to Swift as one of her 'dragons'.

Baldoni also claimed that Swift was present at a pivotal meeting about the movie, held by Lively and Reynolds at their New York penthouse. For her part, a source close to Swift has said that she simply arrived to find the meeting underway and had no involvement. 

The whole saga reportedly left Swift feeling 'used' by Lively, and she subsequently took a 'step back' from their relationship.

But, while all parties deny the allegations against them, the ugly suggestion is that Swift had more involvement in the production of It Ends With Us than she would like people to know. 

It has even been claimed that she personally approved the casting of actress Isabela Ferrer as the younger version of Lily Bloom (Lively's character).

Swift fervently denies this. 

'Speculation that Taylor chose young Lily in casting is simply untrue,' the Daily Mail has learned. 'This subpoena delves into events and things that did not occur.'

That chimes with a statement released on Friday, moments after Swift was subpoenaed as a witness.

'Taylor Swift never set foot on the set of this movie, she was not involved in any casting or creative decisions, she did not score the film, she never saw an edit or made any notes on the film, she did not even see "It Ends With Us" until weeks after its public release,' a spokesperson for Swift said. 'The connection Taylor had to this film was permitting the use of one song, "My Tears Ricochet" [on the soundtrack].'

The Daily Mail has learned that Swift was left devastated on Friday when she was subpoenaed as a witness in the case between Blake Lively and Justin Baldoni  

It is understood that Swift has been 'completely floored' by the legal escalation and is now 'very upset'. And not least because she feels betrayed and 'exploited' by her longtime friend, Lively

It is perhaps understandable then that Swift feels so aggrieved at being thrust to the center of a rancorous legal fight over a film that she maintains she had no part in.

And while it is Baldoni's lawyer, Bryan Freedman, who subpoenaed Swift, the Daily Mail understands that the exasperated singer blames Lively for her unwanted involvement. 

'Taylor has been aware that Blake has been exploiting her name for a while now, but this subpoena takes it to a whole new level,' we have learned.

It is tragic and surely unrecoverable end to a friendship that has spanned a decade.  But, however reluctant she may be, when it comes to the raging It Ends With Us legal battle, this might only be the beginning for Swift.

Representatives for Lively did not respond to requests for comment. 

But, in a statement relating to Friday's subpoena, a spokesperson for Lively said: 'Mr Baldoni [continues] to turn a case of sexual harassment and retaliation into entertainment for the tabloids, going as far as suggesting that they sell tickets to a concert venue - Madison Square Garden - to witness Ms. Lively’s deposition, to subpoenaing Taylor Swift, a woman who has given a voice to millions the world over.'