The event was reportedly touted as a surprise 44th birthday bash for Theroux, with guests including Aniston's former Friends co-star Lisa Kudrow, pal and comedienne Chelsea Handler and U.S. shock jock Howard Stern all photographed arriving at the stars' Bel Air mansion.

However, eagle-eyed paparazzi also spotted a man dressed as a reverend and carrying a Bible enter the home, while catering staff were also seen transporting a large cake featuring likenesses of the couple on top.

The preparations suggest the party was more than just a birthday celebration, but Aniston's spokesperson isn't giving up any information.

A telling statement issued to GossipCop.com reads: "If Jen and Justin feel the need to respond to tabloid and media guess work about a private party held at their home they will let me know. In the meantime, they will remain private like they usually do."

Theroux actually turns 44 on Monday (10Aug15).

The couple has been engaged since 2013.

If the marriage reports are true, it will mark Aniston's second union - she was previously married to Brad Pitt from 2000 to 2005.