postgres: reset pg_last_xact_replay_timestamp()

We have a pg10 replica that got promoted to master and have monitoring around the following query to monitor replication

SELECT EXTRACT(EPOCH FROM (now() - pg_last_xact_replay_timestamp())) as lag

That works great but it got promoted and that state seems like it’s still there so it seems that host which is the main now has a 40000s replication delay.

So looking for a way to remove that stat so it’s not there or reports as 0s