Paris Hilton shared a sweet birthday tribute for Britney Spears on Saturday.

The socialite took to Instagram to wish the pop icon a happy 42nd birthday and shared a series of throwback photos of the pair together in the 2000s.

In her caption, she noted that she and her longtime pal have had ‘so many fun memories together’.

‘Love you so much,’ she gushed as she addressed the Toxic hitmaker directly. ‘Sending you lots of love on your special day.’

The 42-year-old entrepreneur ended off her sweet note and wrote: ‘Keep shining sis’.

In celebration of her birthday, Spears spent the day with mother, Lynne, as the pair appear to now be on good terms after years of being estranged following her 13-year conservatorship.

Spears and Hilton have had a long history of friendship dating back to their days of partying with Lindsay Lohan in the mid-2000’s.

Hilton has been consistently supportive of Spears over the years and has been a frequent presence in her friend’s Instagram comments.

The songstress even gushed over the Simple Life star and said she was one of the ‘kindest’ people she’s ever met in her memoir, The Woman in Me.

During an appearance on Kelly Clarkson’s talk show in late November, Hilton recalled ‘crying’ when she read about the things Spears wrote about her.

Clarkson noted that Spears had written in her tell-all that ‘one of the people who was kindest to me when I really needed kindness was Paris Hilton’.

Spears had also written that Hilton ‘encouraged me to have fun for the first time in a long time.’

In response, Hilton — who also released a memoir earlier this year — said it ‘meant a lot’ to her.

‘I was crying when I read that,’ she said. ‘That really touched me.’

She continued gushing about her pal: ‘She’s just so strong. I love her so much, and I’m just so proud of her for speaking her truth and writing this whole book.

‘That quote meant a lot to me when I read it,’ she added.

Hilton even channeled Spears and dressed up as her for Halloween this past October.

For one of her costumes, she wore the same outfit Spears wore in her iconic Toxic music video.