[Python] How to convert datetime object to milliseconds

I am parsing datetime values as follows:

df['actualDateTime'] = pd.to_datetime(df['actualDateTime'])


How can I convert this datetime objects to milliseconds?

I didn't see mention of milliseconds in the doc of to_datetime.

Update (Based on feedback): This is the current version of the code that provides error TypeError: Cannot convert input to Timestamp. The column Date3 must contain milliseconds (as a numeric equivalent of a datetime object).

import pandas as pd
import time

s1 = {'Date' : ['2015-10-20T07:21:00.000','2015-10-19T07:18:00.000','2015-10-19T07:15:00.000']}

df = pd.DataFrame(s1)

df['Date2'] = pd.to_datetime(df['Date'])

t = pd.Timestamp(df['Date2'])

df['Date3'] = time.mktime(t.timetuple())

print df

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